1. Field of the Invention
The present invention relates to an optical waveguide device, a method of manufacturing the optical waveguide device, and optical communication equipment, and more particularly, to an optical waveguide device for executing modulation and switching by changing the refractive index of cores making use of a thermo-optical effect or an electro-optical effect.
2. Description of the Related Art
In optical communications capable of transmitting data in a large amount at high speed, optical fiber cables are mainly used in a transmission network. Further, an optical waveguide and an optical waveguide device, which is composed of an optical waveguide having functions of switching and modulation added thereto, are used at a point where optical fiber cables are connected to each other according to the use of the point.
FIG. 1 shows a schematic perspective view of an optical waveguide device 1 (1×8 optical switch) used conventionally. The optical waveguide device 1 shown in FIG. 1 is composed of a substrate 2, a lower cladding layer 3, cores 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i, 5j, 5k, 5l, 5m, 5n, and 5o formed in the inside of the lower cladding layer 3 an upper cladding layer 4 covering these cores 5a to 5o, heaters 8a and 8b disposed above the branch portions of the cores, and the like. The cores 5a to 5o, the lower cladding layer 3 and the upper cladding layer 4 are composed of a resin and the like having a relatively high refractive index. Further, the cores 5a to 5o is composed of a material having a refractive index higher than that of the upper and lower cladding layers 4 and
The optical waveguide device 1 shown in FIG. 1 is used by connecting a core end surface 6a to an optical fiber cable, a light emitting device, and the like and by connecting core end surfaces 6b to 6i to optical fiber cables and light receiving devices. Light incident on the core end surface 6a is propagated in the inside of the core 5a, passes through branch portions at three positions, and outgoes from selected one or a plurality of the core end surfaces 6b to 6i. 
In the optical waveguide device 1, it is possible to select a direction in which light travels at the branch portions of the cores. Such a scheme will be briefly explained below. FIG. 2 shows a plan view in which a part of the optical waveguide device 1 is enlarged. The light incident from the core end surface 6a is propagated in the inside of the core 5a and reaches the branch portion of the cores 5b and 5c. As shown in FIG. 3 which is an A-A sectional view of FIG. 1, the heaters 8a and 8b are disposed on the surface of the upper cladding layer 4 on the cores 5b and 5c, the core 5a is heated by heating the heater 8a, and the core 5c is heated by heating the heater 8b. 
If the core 5c is heated by the heater 8b, the effective refractive index of the core 5c is reduced. Since the light, which has been propagated in the core 5a, is propagated to a core having a higher effective refractive index, if the heater 8b is heated, the light is not propagated in the core 5c and is propagated only in the core 5b. Further, if any of the the heaters 8a and 8b is not heated, the light can be propagated in both the cores 5b and 5c. As described above, since the refractive indices of the cores are varied by a temperature, the propagatrion of light in a core can be controlled by varying the refractive index of the core by turning on and off a heater just below the core.
Although the light having been propagated in the core 5b further reaches the branch portion of the cores 5d and 5e, the light can be propagated in any one of the cores 5d and 5e by heating any one of the heaters 8a and 8b. Further, if any of the the heaters 8a and 8b is heated, the light can be propagated in both the cores 5d and 5e. 
Increasing employment of the optical waveguide device that has the switching function is hereinafter expected in various fields such as when data is transmitted from one data transmission source to many terminals and when maintenance and inspection are executed to an ordinarily used cable by switching it to another cable.
However, conventional optical waveguide devices have the following problems. To manufacture the optical waveguide device 1 shown in FIGS. 1 and 2, first, an optical waveguide, which is composed of the lower cladding layer 3, the cores 5a to 5o, and the upper cladding layer 4, is formed on the substrate 2, a metal thin film is vapor deposited on the upper cladding layer 4, and the heaters 8a and 8b are formed by masking the portions, to which the heaters 8a and 8b are formed by etching. Further, a pair of wire bond pads 9a and 9b for connecting the respective heaters 8a and 8b to a power supply and wiring for connecting the heaters 8a and 8b to the wire bond pads 9a and 9b are also formed on the upper cladding layer 4 by applying vapor deposition and etching.
In the method of manufacturing the optical waveguide device as described above, when the vapor deposited metal thin film is etched, there is a problem in that the upper and lower cladding layers 4 and 3 are also etched as shown in FIG. 4 or that the upper cladding layer 4 and the cores 5b and 5c are degraded by the effect of heat in the vapor deposition and a chemical agent used in the etching and thereby the performance of the optical waveguide device 1 is varied. Further, many manufacturing processes are additionally required to avoid the restriction due to the heat in the vapor deposition and the chemical agent used in the etching, from which a problem also arises in that a longer time and more expensive cost are required to manufacture the optical waveguide device.
Since the heaters 8a and 8b are formed on the surface of the upper cladding layer 4 in the conventional optical waveguide device, if a high temperature is applied to vapor deposit the heaters 8a and 8b, there is a possibility that the cores 5a and 5b are degraded, thereby a process for forming the heaters 8a and 8b are restricted. Accordingly, there is a problem that the heaters 8a and 8b are liable to be exfoliated from the upper cladding layer 4. Since the heaters 8a and 8b are only vapor deposited on the surface of the upper cladding layer 4, a problem also arises in that the heaters 8a and 8b are exfoliated by moisture and by heat generated when they are used.
Further, if the cores and the heaters are densely disposed in a small space, the wiring for connecting the heaters 8a and 8b to the wire bond pads 9a to 9d traverses over the cores 5b to 5g. If the cores are located in the vicinity of the wiring, the heat generated by the wiring and the change of an electric field and a magnetic field caused by a current flowing through the wiring apply an unexpected effect on the light propagated in the cores 5b to 5g. Accordingly, the cores must be prevented from being affected by the heat generated in the wiring and by the change of the electric field and the magnetic fields by being disposed at positions sufficiently separated from the wiring. To sufficiently and effectively heat only a particular core by a heater, the heater must be positioned near to the core by reducing the thickness of the upper cladding layer. However, it is impossible to position the heaters near to the cores as well as to separate the cores from the wiring of the heaters and electrodes in the conventional manufacturing method of the optical waveguide device in which the heaters, the wiring, and the electrodes are formed on the same surface.